The present invention relates to image screens; more particularly, this disclosure provides a rear projection screen having anti-reflective layer and a method of forming and aligning that anti-reflective layer.
Image screens can be of various types, including rear projection screens, image generating screens and front projection screens. Rear projection screens in particular are illuminated from behind, with a visible image being dispersed by the screen itself to viewers in front of the projection screen. Image generating screens are similar to rear projection screens, since light is normally generated behind the front surface of the screen and is dispersed through the front surface of the screen to viewers within a desired viewing angle. Finally, front projection screens are illuminated from in front of the projection screen, e.g., the viewers and projection device are positioned on the same side of the screen.
Often, image screens are viewed in the presence of light which can reflect against the screen and detract from image quality. Television screens, for example, can include glass or plastic elements that reflect ambient light and reduce image contrast. As a result of these problems, some recent design efforts have focused on developing projection screens with reduced reflectivity of ambient light.
One method of reducing screen surface reflectivity, and thereby increasing the screen""s contrast, involves the use of black strips which define opaque areas of the projection screen to reduce reflection of ambient light. In the context of rear projection screens, the projection image is redirected through a lens array on the back side of the screen, to concentrate projection light onto transmissive areas of the screen and generally around the black strips. The black strips are relatively thin, and generally do not perceptibly interfere with a viewer""s perception of an image projected on the screen.
While the solution generally described above is satisfactory for its intended purpose, there are a number of shortcomings in this solution. For example, a pattern of black strips or other anti-reflective material must usually be precisely aligned to the transmissive areas so as to not degrade screen brightness, and such alignment is difficult. Also, the black strips typically only cover a small area of the total projection screen. As an example, a typical television screen might have black strips covering less than forty percent of the total screen area. A result of this latter shortcoming is that screen reflectance is often undesirably large despite the presence of the black strips.
FIGS. 1-3 are used to generally explain these shortcomings. In particular, FIG. 1 shows a cross section of a projection television (TV) screen 11 having an image source 13 and a projection screen 15 that disperses image light to viewers within a desired field of view. The projection screen includes a Fresnel lens 17 which receives light beams 27 from the image source and redirects the light beams in a manner such that they traverse a direction perpendicular to the screen. Light passing through the Fresnel lens then strikes an array of lenses 19, which are seen in FIG. 1 to be semi-cylindrical column lenses that vertically span the interior of the projection screen 15. These lenses redirect light from the image source to transmissive columns formed around xe2x80x9cblack stripxe2x80x9d areas 23, mounted to the screen""s main body 21. The screen also usually includes a dispersing element (not seen in FIG. 1), which vertically scatters light focused by the array of lenses for end viewing.
FIG. 2 presents a perspective view of the viewer-side 28 of the TV screen of FIG. 1. In particular, the screen 15 is often oriented such that the black strips 23 extend vertically from the top of the screen to the bottom of the screen. The light source (not seen in FIG. 2) forms an image against the back side 30 of the screen. FIG. 2 also shows a light bulb 31, which represents a source of ambient light 33 against the viewer-side 28 of the projection screen. The black strips are used to reduce reflected light 35 from degrading image contrast.
As shown in FIG. 3, the lenses 19 focus light toward an aperture and focal region, ideally around the black strips 23. However, it is usually difficult to precisely align the black strips with these optical paths, and the result is often that the black strips need to be placed relatively far apart, such that the portion of the screen covered by anti-reflective material (xe2x80x9cCxe2x80x9d/xe2x80x9cCxe2x80x9d+xe2x80x9cBxe2x80x9d) is often much less than fifty percent of total screen area. Further still, the black strips and transmissive areas for the optical paths are often made relatively large for ease of alignment, rendering it difficult to achieve certain efficiencies in anti-reflectance that might be gained if the transmissive areas were made quite small. The alignment problem can be compounded when a scattering layer 37 or viewer-side array of cylindrical lenses 38 is employed in the screen to disperse light.
A definite need exists for an image screen that maintains high image contrast. More particularly, a need exists for an image screen which significantly reduces reflection of ambient light on the viewer-side of the screen. Further still, a need exists for a method of forming and efficiently aligning an anti-reflective layer with non-transmissive areas of the screen, ideally such that the anti-reflective layer occupies a very substantial portion of total screen area without significantly detracting from screen brightness or reducing image contrast. The present invention satisfies these needs and provides further, related advantages.
The present invention solves the aforementioned needs by providing an image screen having an anti-reflective layer formed using the optical pattern of the screen itself. By using projection light to define the contours of the anti-reflective and transmissive areas, the present invention provides for a precise xe2x80x9cblack stripxe2x80x9d or xe2x80x9cblack layerxe2x80x9d alignment mechanism, such that almost all of the screen can be layered with an anti-reflective layer while maintaining image brightness. Further still, it is expected that as much as ninety-nine percent or more of the screen can be made reflection resistant in this manner, improving the image contrast by substantially reducing conflict with ambient light. It is expected that the present invention will find wide application to projection television and similar systems.
One form of the invention provides a method of forming an anti-reflective layer in or on an image screen. This method calls for using lens elements of the screen to shine light toward the screen""s front surface. The optical pattern formed in this manner is used to place a reflection resistant material upon the screen in all locations, except those portions of the screen that substantially correspond with the primary optical paths of projection light through the screen. In more detailed features of this form of the invention, the material can be created using a photoresist which is adhered to the screen and then exposed and developed by projection through the lens elements to remove photoresist material at screen locations not receptive to projection light; a black anti-reflective layer is then deposited on top of the screen, with exposed photoresist subsequently being removed to leave the anti-reflective layer in the non-transmissive areas. Alternatively, projection light can be used to provide relative charge to areas that should not be transparent to light, and a material can then be applied which sticks to charged areas of the screen, such that the material remains upon all portions of the screen except the transmissive portions. In each of these more detailed aspects of the invention, transmissive portions of the screen closely align with the primary optical paths of light to be transmitted through the image screen during the screen""s normal use.
A second form of the invention provides an image screen having an anti-reflective layer created using the focal pattern of the screen, while a third form of the invention provides an improvement in screen fabrication.
In more detailed features of the invention, the anti-reflective layer is formed to have pinholes through which projected light travels; the pinholes closely align with projection light, and so, the anti-reflective surface can be formed to very accurately cover most all of the screen that does not transmit light. In this manner, it is expected that in some applications, ninety percent or more of the screen""s surface may be made resistant to reflection of ambient light.
The invention may be better understood by referring to the following detailed description, which should be read in conjunction with the accompanying drawings. The detailed description of a particular preferred embodiment, set out below to enable one to build and use one particular implementation of the invention, is not intended to limit the enumerated claims, but to serve as a particular example thereof.